Tetrapyrrole pigments have been determined in various fractions of the benzene-methanol bitumoid by means of absorption spectra for these sediments, which range from Recent muds to Late Cretaceous beds. The Holocene-Pleistocene muds contain mainly chlorins, including oxidized forms (purpurins), in which the spectrum has an additional peak in the long-wave region (690-700 nm). All the sediments below the base of the Miocene, apart from the black-shale bands (Albian to Santonian), are low in organic matter and virtually free from tetrapyrrole pigments. Copper and nickel porphyrins in the DPEP and etio series represent the main forms of pigment in the black shales. There is also an oxidized porphyrin: tetrapyrrole-586. The etio type and the tetrapyrrole-586 may have been formed by aromatization from oxidized chlorins produced by early diagenesis from chlorophyll derivatives. That route appears more likely than thermal production because there are chlorins along with porphyrins at considerable depths (>1000 m below the ocean floor), so the thermal setting has been mild throughout the basin history.